Ruth Burstein

External load can alter the energy cost of prolonged exercise

SummaryThe present study was undertaken to examine the energy cost of prolonged walking while carrying a backpack load. Six trained subjects were tested while walking for 120 min on a treadmill at a speed of 1.25 m · s−1 and 5% elevation with a well fitted backpack load of 25 and 40 kg alternately. Carrying 40 kg elicited a significantly higher (p<0.01) enery cost than 25 kg. Furthermore, whereas carrying 25 kg resulted in a constant energy cost, 40 kg yielded a highly significant (p<0.05) increase in energy cost over time. The study implies that increase in load causes physical fatigue, once work intensity is higher than 50% maximal work capacity. This is probably due to altered locomotion biomechanics which in turn lead to the increase in energy cost. Finally, the prediction model which estimates energy cost while carrying loads should be used with some caution when applied to heavy loads and long duration of exercise, since it might underestimate the acutal enery cost.

The effect of caffeine ingestion on physical performance after prolonged exercise

SummaryThe purpose of this study was to determine the effect of caffeine ingestion on physical performance after prolonged endurance exercise. Twenty three trained male volunteers participated in a 40-km march and were divided into two groups, matched for caffeine clearance rate and aerobic capacity. The experimental group ingested, prior to the march, a caffeinated drink at a dose of 5 mg·kg−1 body mass and at the 3rd and 5th h of marching an additional drink at a dose of 2.5 mg·kg−1 body mass. The control group ingested a drink of equal volume at the same times. Upon termination of the march each subject performed a cycle ergometer test at an intensity of 90% maximal oxygen consumption. Time to exhaustion and rate of perceived exertion (RPE) were recorded. Blood samples were drawn predrink, at the 3rd and 5th h of marching and immediately after the cycle ergometer test, and were analysed for caffeine, free fatty acids (FFA), lactate and glucose levels. Plasma FFA levels increased during the march (p<0.05), with no significant difference between groups. Lactate levels increased in the experimental group (p<0.05), with no significant change in the control group. Glucose levels did not change significantly in either group. After the cycle ergometer test, lactate levels were significantly higher in the experimental, as compared to the control group (3.77±0.33 vs 2.52±0.35 mmol·l−1, respectively). There was no significant difference between treatments in the time to exhaustion on the cycle ergometer, but RPE was different (p<0.05). Under the conditions of this study, the results do not indicate caffeine ingestion as an ergogenic aid which will postpone exhaustion following prolonged endurance exercise.

Lipoprotein profile changes during intense training of Israeli military recruits

The effect of prolonged strenuous military training on serum lipoproteins was studied in 73 new recruits. Dietary intake, body weight, and average energy expenditure were recorded, and blood samples collected at three time periods before training began (time 0), and after 6 and 12 wk of intense physical activity (times I and II, respectively). There was a significant increase in high density lipoprotein (HDL) cholesterol and a decrease in low density lipoprotein (LDL) cholesterol accompanying an increase of duration and intensity of exercise. HDL increased from 40.5 +/- 7.7 mg.dl-1 at time 0 to 44.5 +/- 9.4 mg.dl-1 at time I and to 52.8 +/- 8.7 mg.dl-1 at time II, and each mean P-value for increases in HDL from time 0-I, I-II, and 0-II were P < 0.0001). For LDL cholesterol, the mean decreases were -1.1, -6.1, and -7.3 mg.dl-1, respectively (P = 0.003 from I-II, and 0.01 from 0-II). These changes did not correlate with weight loss, reduced energy, or fat intake. We conclude that intense physical activity is associated with beneficial changes in the lipoprotein profile in new military recruits during a training period extending over 12 wk.

Effect of fluid intake on renal function during exercise in the cold

SummaryThe effect of an imposed drinking discipline versus ad libitum drinking was studied on 21 healthy, well-trained volunteers, during a continuous 4.5-h march at an altitude of 1,700 m and an ambient temperature of 0° C, SD 1. Group I (n = 13) was instructed to drink 250 ml of warmed, artificially sweetened fluid every 30 min, whereas group II (n = 8) drank plain water ad libitum. The median fluid intake in group I was significantly higher than in group II (P < 0.0002). Serum urea and osmolality decreased during the march in group I (P < 0.05; P < 0.002, respectively) with no significant change in group II. In both groups, a similar increase in haemoglobin concentration concomitant with a reduction in calculated blood and plasma volume was observed after exercise and did not correlate with the state of hydration. Total urine volume, creatinine clearance, urea clearance and potassium excretion were significantly higher and urinary osmolality was lower in group I than in group II (P < 0.05). These results reflect a state of extreme “voluntary dehydration” in the control group when no fluid intake was obligatory. Thus, during exercise in the cold, under conditions similar to those in this study, a fluid intake of 150 ml · h−1 should be maintained in order to keep a urinary flow of about 1 ml · kg−1 · h−1 and to achieve a good state of hydration.

Glucose polymer ingestion : effect on fluid balance and glycemic state during a 4-d march

The effect of glucose-polymer solution on physical performance has been extensively studied under controlled laboratory conditions. The present study was conducted to investigate the influence of such beverages on fluid balance and on glycemic state during a moderate, prolonged field exercise. Forty-eight endurance trained, male subjects participated in the study. The maneuver consisted of a 4-d march; 29, 39, 36, 30 km.d-1, at a speed of 5-6 km.h-1. The subjects covered a total distance of 134 km at an estimated exercise intensity of approximately 40% VO2max, under hot climate conditions (ambient temperature, 32-41 degrees C; relative humidity, 60-14%). Subjects were randomly assigned to one of two groups: glucose polymer-electrolyte beverage (GP; N = 24) and tap water (TW; N = 24). Each group was then divided into two subgroups consuming fluid ad libitum (TWa, GPa) or instructed to consume 900 ml.h-1 (TWb, GPb). The mean daily fluid consumption of all subgroups was similar (5252 +/- 229 and 4640 +/- 67 ml in TWa and TWb; 5257 +/- 317 and 5253 +/- 216 ml in GPa and GPb, respectively). Weight loss, reflecting the degree of dehydration, was 1.2 +/- 0.1% and 1.9 +/- 0.3% of initial body weight in TW and GP, respectively. On day 1, plasma volume changed by +0.4% and -1.8% in the TW and GP groups, respectively. On the days 2-4 changes in both groups were similar.(ABSTRACT TRUNCATED AT 250 WORDS)

Prediction of physical performance through muscle enzymes activity

SummaryPhysical performance deteriorates during strenuous exercise as manifested by a decrease in maximal aerobic power and increased activity of serum muscle enzymes. The relationship between these parameters was investigated in 41 trained subjects during 24 h marches and the following recovery period. Peak O2 uptake and serum activity of creatine phosphokinase (CPK) and glutamic oxalacetic transaminase (GOT) were measured. During the marches there was a simultaneous, significant elevation in serum CPK and GOT activity and a significant reduction in peak O2 uptake. During the early recovery period (24 h) no significant changes occurred in muscle enzyme activity and peak O2 uptake; thereafter (up to 72 h after the end of the march), a gradual decline in enzyme activity levels with a concomitant increase in peak O2 uptake was observed, reaching pre-march values. A “mirror image” relationship between muscle enzyme activity and peak O2 uptake was found during three clearly distinguished phases: a) 24 h march, b) early recovery stage and c) late recovery stage. These findings suggest, that muscle enzyme leakage from muscle cells is closely related to the decline in muscular function and aerobic power. Thus, muscle enzyme activity might be a practical measure of physical performance capacity during the early and late stages of recovery from prolonged endurance exercise.

Chronic colchicine treatment does not impair glucose tolerance in familial Mediterranean fever patients.

AbstractObjective: To investigate a long-term colchicine treatment in inhibiting normal release of insulin, in response to a glucose load. Setting: The Heller Institute of Medical Research, Sheba Medical Center, Tel-Hashomer. Patients: Thirty-one familial Mediterranean fever (FMF) patients, treated continuously with colchicine (1.0–2.0 mg · day–1) for 2–13 years. Methods: A standard oral glucose tolerance test (OGTT) was performed to study the effect of long-term colchicine treatment on glucose-induced insulin response. An intravenous glucose tolerance test (IVGTT) was then performed on randomly chosen FMF patients (n = 9) and age-matched controls (n = 5). Glucose was administered 30 min after intravenous colchicine (2 mg) infusion. The sum of 1st- and 3rd-min insulin levels served as an index of early-phase insulin release. Results: Based on the Office Guide to Diagnosis of Glucose Intolerance [13], one subject exhibited impaired glucose tolerance and two others had abnormal dynamics of glucose during the test but normal values at 120 min. Insulin values were normal in all participants. No significant differences were found in maximal glucose and insulin concentration, nor in the insulin release index between FMF colchicine-treated and healthy controls. Conclusions: Based on these findings, no impairment in glucose dynamics could be demonstrated in chronically colchicine treated patients, compared to untreated controls.

The relationship between short-term antibiotic treatments and fatigue in healthy individuals

SummaryAntibiotic treatment tends sometimes to result in sensations of fatigue and decreased physical performance. The effects of antibiotics were therefore studied in 50 healthy, male trainees, aged 18–25 years, assigned in a random, double-blind fashion to one of the following treatments: tetracycline, ampicillin, trimethoprim/sulphamethoxazole, placebo I and placebo II. Duration of treatment was five times the half-life of each agent and the placebo was matched accordingly. Muscle enzyme activity (serum glutamine oxaloacetate transaminase, lactate dehydrogenase, creatine phosphokinase), maximal aerobic capacity (

Hyponatremia induced by exercise: a 24-hour endurance march study.

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